The present invention relates generally to non-return check valves and, in particular, to an adjustable flow poppet valve for use at the nozzle of an injection molding apparatus.
Typically, bulk plastic material is fed into an extruder or injection molding machine or a blow molder through a barrel or cylinder utilizing a rotating helical screw. Such a machine is operated at an elevated temperature and, if it is required to be shut down, the plastic material tends to solidify.
Typically, a check or poppet valve is installed between the feedscrew and the nozzle of an injection molding machine to control the plastic material flow during each cycle. When the feedscrew is operated to force material through the nozzle, the pressure of the advancing material forces the check valve open and plastic material flows through the check valve and through the nozzle to supply the associated mold. When the desired amount of plastic material has flowed into the mold, the feedscrew is moved forward in an injection stroke forcing the poppet in the poppet valve to move in a rearward direction closing the valve and preventing back flow of the material.
One form of non-return check valve used for an injection molding machine is disclosed in U.S. Pat. No. 3,438,393. The check valve has a moveable member with a first sealing portion supported in a main valve body having a second sealing portion, the moveable member being moveable between a first position in which the sealing portions cooperate to prevent the flow of thermoplastic material past the moveable member, and a second position in which the sealing portions are spaced to allow flow of thermoplastic material past the moveable member. The moveable member has a stop portion, and a retaining member is located in the path of the stop portion, spaced forwardly of the stop portion when the moveable member is in its first position so as to prevent forward movement of the moveable member beyond its second position. A retaining portion or passage in the main valve body loosely holds or retains the retaining member in the main valve body while being substantially larger than the retaining member to allow substantial flow of thermoplastic material between the walls of the passage and retaining member. The retaining passage can be a bore, the retaining member can be a pin located in the bore and spaced from its inside surface and a moveable groove poppet can be provided, the pin passing through the poppet, the front of the poppet acting as an injection head.